Those in the textile industry have long recognized the value in treating the entire surface area of each individual filament in a multifilament yarn. The industry has unsuccessfully tried to develop methods and apparatus to overcome the issues surrounding such surface treatment. In fact, many multifilament applications have dealt with the issue simply by treating the individual filament surfaces prior to creating the multifilament yarn; however, this individual surface treatment is not economically practical in most applications.
In the past, the textile industry has generally dealt with treating the surface of individual filaments of a multifilament yarn by submerging the yarn in a tank of treatment solution while the yarn is under no tension, or only enough tension to gradually move the yarn through the tank. Using this method, the yarn was left in the tank for an extended period of time to allow the treatment solution to penetrate past the outermost filaments and wet the innermost fibers.
The traditional method of treating multifilament yarns has many drawbacks. The most apparent drawback is that the method can be extremely slow as the yarn must be submerged in the treatment tank for a long period of time and cannot travel at any appreciable speed through the tank. Additionally, the extended exposure time required to treat the innermost filaments of the yarn subjects the outermost filaments to possible overexposure. For instance, it is often desirable to clean and etch the outer surfaces of the individual filaments of the multifilament yarn with an acidic solution. Using traditional treatment methods the outermost filaments may be subjected to the acidic solution significantly longer than the innermost filaments resulting in non-uniform etching and reduced filament strength.
Another significant drawback of this method is that surfactants are generally required to lower the surface tension of the treatment solution, and reduce the interfacial tension between the treatment solution and the filaments, thereby promoting wetting of the filaments. Surfactants introduce additional costs and difficulties in the surface treatment process. Yet a further drawback is that the yarn can become tangled in the treatment solution because it has to essentially float through the solution under little, or no, tension. This free floating aspect of the process further limits the processing speed in that additional measures that may improve the surface coating of the filaments, such as agitation of the solution and the yarn, cannot be implemented due to the increased likelihood of yarn entanglement.
The art has needed an improved method of treating the surfaces of the individual filaments of multifilament yarns that increases the processing speed, reduces reliance on surfactants, and provides increased uniformity of the surface treatment of inner filaments and outer filaments of the multifilament yarn. The method and apparatus of the present invention provides these desired qualities and significantly improves the state of the art of surface treatment of filament surfaces in multifilament yarns. With these capabilities taken into consideration, the instant invention addresses many of the shortcomings of the prior art and offers significant benefits heretofore unavailable.